The present invention relates to subterranean operations, and more particularly, to set-delayed cement compositions and methods of using such cement compositions in subterranean applications.
Hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
A broad variety of cement compositions have been used in conventional subterranean cementing operations, including, inter alia, cement compositions comprising Portland cement, and cement compositions comprising water, fly ash, and lime. However, the composition and quality of both Portland cement and fly ash vary widely. Accordingly, the set times of conventional cement compositions employing Portland cement and/or fly ash may be unpredictable. This may be problematic because, inter alia, it may cause such conventional cement compositions to set prematurely, before they have been properly placed in a desired location in a subterranean formation.